Actually the 90% white wasn't really so homogeneous but what mattered was the sub-groups were prepared to integrate. Granddaddy Drumpf did not keep insisting the Kaiser was the good guy in WW1.
What messed up was post-1965 Latinx importing which USA Inc thought was just an extension of the Trans-Atlantic white movement from 1870-1930. In other words Daddy Cruz = Granddaddy Drumpf
Unfortunately they brought in lots of white Latinx who had earlier re-engineered their own minds to claim native status and to regard the USA as the enemy. The mentality was to blame all the problems of colonialism on white Anglos who had almost nothing to do with what happened much earlier.
Once the Latinx came in large numbers, socio-political divisions similar to their home countries, including their former overlords Portugal and Spain, were brought in.
As late as 1930s-1970s, the Iberian countries were still ruled by military dictatorships Same for a sizable chunk of their ex-colonies.
While Anglo whites maintained a stable political system in USA & Canada, the list of presidents in these Latinx countries is incredibly long, indicating the amount of civil strife, internal rebellions, class and regional differences.
The current cartel culture in which bosses are the feudal lords until they are bumped off by rivals is an extension of the historic Spanish-Latinx system.